In the parent application it was disclosed that coal could be subjected to pyrolysis or hydropyrolysis under certain conditions to produce a particulate char and a liquid organic fraction which is rich in hydrocarbons, completely combustible, can be beneficiated and can serve as a liquid phase for a carbonaceous slurry fuel system. Thus the viscosity, pumpability and stability of the slurry when the char is admixed with the liquid organic fraction is a function of pyrolysis process parameters, the means of slurrying, the loading and the stabilizers used as well as the physical aspects of the solid constituent.
As set forth in the parent application, the feasibility of economically transporting slurry fuel is predicated upon its rheology. Rheology is the study of deformation and flow of matter. It is concerned primarily with the mechanics of deformable liquids or solids. The study of rheology is complicated by nonideal behavior. A liquid whose viscosity decreases with increasing stress (such as increased rate of flow or of stirring) is called pseudoplastic; if the viscosity increases with the stress, the liquid is dilatant. An ideal elastic solid shows no shear at any shearing stress, but actual solids will have a yield point beyond which flow begins to occur. A solid is known as a Bingham plastic if, once flow takes place, the rate of shear is proportional to the shearing stress in excess of the yield value.
The measured viscosity of a system is given by a ratio as a function of shear. A Newtonian fluid is one whose viscosity coefficient is independent of shear. Thus, Bingham and pseudoplastic solids as well as non-Newtonian liquids have viscosities that are dependent on the rate of shear.
The situation becomes considerably more complicated since the measured viscosity can vary with time as well as with shearing stress. A liquid which becomes more fluid with increasing time of flow is said to be thixotropic, while if the opposite is true, the liquid is said to exhibit rheopexy. Examples of these types of behavior are as follows: Gases and pure single-phase liquids exhibit Newtonian viscosity, while suspensions, slurries and emulsions are apt to show dilatant behavior--a common example being that of a thick starch paste. Household paints are often pseudoplastic so as to brush easily but not run; the same is true for printing inks. Some gels are thixotropic--they will liquify on shaking.
In most prior art slurries, the rheology characteristics could not be varied greatly to accomodate certain end-use applications or transportation systems. For example, the rheology of water/coal or CO.sub.2 / coal systems is a function primarily of loading. Even with alcohol or oil media, variance of the liquid viscosity is not practical.
As disclosed in the parent application, the novel fuel system exhibits some very advantageous rheology properties and, more importantly, the means for varying these rheology characteristics for end-use application or a particular pumping system. In many cases, it is pseudoplastic and even thixotropic. This allows storage of the slurry which is readily pumpable. These rheology characteristics are a function of the characteristics of the liquid, including its viscosity, the characteristics of the solid, including its shape, and the interaction of stabilizers. It will be realized that the rheology of any given slurry admixture is empirical. However, the instant invention is concerned with efficient methods of varying the rheology of the slurry to tailor the slurry to specific transport systems as well as end-use applications.